1. Field of the Invention
The present invention relates to an image sensing apparatus having the photoelectric conversion function.
2. Related Background Art
A film screen system as a combination of an intensifying screen with an X-ray photograph film is often used for X-ray sensing intended for medical diagnosis.
In this method, X-rays having passed through the subject include information about the interior of the subject, they are converted to visible light proportional to the intensity of the X-rays by the intensifying screen, and the X-ray film is exposed to the visible light.
Recently, use is being started of X-ray digital sensing apparatus for converting X-rays to visible light in proportion to the intensity of the X-rays by a phosphor, converting the visible light to electric signals by use of photoelectric conversion elements, and converting them to digital signals by an A/D converter.
Examples of such apparatus proposed heretofore are the X-ray digital sensing device in which an image sensing device is constructed as a matrix array of elements wherein an amorphous semiconductor is placed between electrodes on a substrate of glass and in which the phosphor for converting X-rays to visible light is further deposited thereon; the X-ray digital sensing device which uses tapered optical fibers obtained by softening a bundle of optical fibers by heat or the like and stretching them and which is composed of two-dimensionally connected modules, each module having such structure that a solid state image sensing device such as a CCD sensor or the like is placed on the narrow side of the tapered shape while the phosphor is deposited on the other side of the tapered optical fiber; and so on.
The X-ray digital sensing devices as described above are mainly utilized for medical diagnosis etc. and, for early discovery of abnormal part and accurate diagnosis, there are increasing demands for higher resolution, lower noise, moving picture, wider sensing area, and so on.
However, the X-ray digital sensors described as the above conventional examples had the following problems.
In the case of the apparatus using the semiconductors comprised of amorphous silicon etc. on the glass substrate, it was possible to set a large photoreceptive area for photoelectric conversion, but it was hard in terms of processes and device characteristics to make the size of pixels finer.
In the case of the apparatus using the solid state image sensing devices of the silicon substrate, such as the CCD sensors or the like, it was possible to make the pixel size finer and it was also easy to perform the sensing of dynamic picture because of the feasibility of high-sensitivity and high-speed driving. It was, however, impossible to realize the large photoreceptive area because of the process constraints.
There are thus sensing systems in which the photoreceptive area is expanded by increasing the number of solid state image sensors by use of optical fibers tapered so as to prevent non-photoreceptive regions of the solid state sensors from overlapping with each other, as illustrated in FIG. 1.
In FIG. 1, reference numeral 1 designates the solid state image sensing devices, each consisting of a photoreceptive area in which a plurality of photoelectric conversion elements are arranged, 4 a scintillator for converting X-rays to light, such as visible light or the like, of wavelengths that can be detected by the photoelectric conversion elements, 8 the tapered optical fibers, 10 protective glass sheets, 11 bonding wires, and 12 ceramic packages.
The tapered optical fibers are, however, expensive and have some thickness and weight. It is thus possible to use several fibers in parallel, but there will arise a problem if they are used in the number enough to obtain the photoreceptive area necessary for sensing of chest part.
These problems made it difficult to realize all the performance including the higher resolution, the dynamic picture, etc., the wider photoreceptive area, the smaller size of apparatus, and the lower cost, demanded for the X-ray digital sensing apparatus for medical diagnosis.
An object of the present invention is to provide an image sensing apparatus of optimum structure for attainment of the wider photoreceptive area.
In order to accomplish the above object, an embodiment of the present invention provides an image sensing apparatus comprising:
a plurality of solid state image sensing devices, each having a photoreceptive area comprising a plurality of photoelectric conversion elements; and
lightguide means comprising a plurality of lightguide portions, each guiding light to a corresponding one of said plurality of solid state image sensing devices,
wherein said lightguide portions comprise a configuration for guiding light obliquely relative to a direction normal to an incident plane of light of said lightguide portions and to the direction where incident light radiates.
The other objects and features of the present invention will become more apparent by the description of the specification and drawings which follows.